1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor memory device, and more particularly, to a method for manufacturing a capacitor having a dielectric film formed of a tantalum oxide film.
2. Description of the Related Art
As the integration degree of a dynamic random access memory (DRAM) increases, methods of increasing the effective area of a capacitor, methods of reducing the thickness of a dielectric film, and methods of increasing the dielectric constant of the dielectric film are used in order to increase the amount of charge accumulated in a restricted cell area.
For example, in a stacked structure comprising a silicon nitride film and a silicon oxide film used as the dielectric film of current highly integrated memory devices, the effective electrical thickness is reduced by physically reducing the thickness of the stacked structure. The limits of the effective electrical thickness of the stacked structure comprising the silicon nitride film and the silicon oxide film are considered to be about 40 .ANG.. A dielectric film having an effective electrical thickness of less than 40A is difficult to deploy in an operating device due to the large leakage current experienced at such thicknesses.
In order to overcome the limits of the stacked silicon nitride and silicon oxide films, dielectric materials with higher dielectric constants are being employed. For example, a tantalum oxide film has a dielectric constant of about 24, which is larger than the dielectric constant of a silicon nitride film, which is about 7. Moreover, ferroelectric materials with dielectric constants of no less than several hundreds are being employed.
The appropriateness of introducing a new dielectric material should be determined based on its suitability for use in conventional processes, probability of stable manufacturing apparatuses, mass productivity, economical efficiency, and stableness of the operation of the device. The tantalum oxide film is known to be the material which most closely satisfies the above requirements.
The electrical characteristics of the tantalum oxide film depend considerably on the processing conditions. In the present invention, optimal processing conditions are described for forming the tantalum oxide film for use as a dielectric film.